1. Field of the Invention
The present invention relates to an information processing apparatus, line noise reduction processing method, and computer-readable storage medium.
2. Description of the Related Art
Diagnoses and treatments based on (moving image) imaging using radiation (for example, X-rays) have been brisk. Recently, an X-ray imaging apparatus using a flat panel detector (in which an amorphous silicon TFT and a semiconductor sensor are formed on a glass substrate) is especially often used. However, the flat panel detector that uses an amorphous silicon TFT cannot amplify a photoelectrically converted signal in a pixel. Instead, accumulated charges are read out via a long signal line. For this reason, noise is readily generated in an image due to the influence of external or internal factors.
Imaging using radiation needs to be done in a low dose to reduce radiation exposure of a human body. Hence, a read signal has a very small value, and only a slight fluctuation in an image is visually recognized. Particularly, stripe-shaped unevenness (to be referred to as line noise hereinafter) running in the vertical or horizontal direction greatly influences a diagnostic image because it is sensitively detected by the human eye.
Conventionally, a technique disclosed in Japanese Patent Laid-Open No. 2003-204955 (to be referred to as reference 1 hereinafter) is known as a line noise reduction method. The method of reference 1 performs high-pass filter processing of an original image containing line noise in a direction perpendicular to the line noise. The processed image then undergoes low-pass filter processing in the horizontal direction. A line noise image is consequently acquired. The line noise image is subtracted from the original image. This allows to reduce the line noise.
The method of reference 1 uses a low-pass filter to remove an object extracted by a high-pass filter. In this case, however, object removal is insufficient, resulting in an edge blur or artifact in the object.
Furthermore, the techniques of reference 1 needs filter processing of all pixels. Since image processing takes time, these methods are not suitable for, for example, a moving image in fluorography.